*3.2. SEM and AFM*

Figure 2 shows SEM images of the (111) face of the diamond before and after irradiation with argon and carbon ions at temperatures of 230 and 650 ◦C, respectively. The radiation fluences in both cases were equal to 1.3 <sup>×</sup> <sup>10</sup><sup>18</sup> ion/cm2. Traces of mechanical polishing are clearly visible on the surface before irradiation, which were removed by high-fluence ion irradiation. At the same time, the ion irradiation led to the appearance of etching pits in the form of equilateral triangles with sides of about 20 μm and open micropores. Such micropores are associated, as a rule, with the increased sputtering of areas of clusters of crystal structure defects, which lower the binding energy of surface atoms. At higher magnification, a stochastic nanoglobular relief appears in the SEM images (insets in Figure 2).

**Figure 2.** SEM images of the (111) face of the diamond: (**a**) before irradiation, (**b**) after irradiation with 30 keV Ar<sup>+</sup> 230 ◦C ions and (**c**) after irradiation with 30 keV C<sup>+</sup> 650 ◦C ions.

The AFM measurements of the relief also show the removal of the traces of mechanical polishing under ion irradiation and the appearance of a stochastic nanorelief (Figure 3). The roughnesses before and after the irradiation of the diamond surface are close; the root-mean-square roughness at a base length of 1 μm is about 20 nm.

**Figure 3.** AFM images of the (111) face of diamond (**a**) before irradiation and (**b**) after Ar<sup>+</sup> ion irradiation with 30 keV at *T* = 230 ◦C.

It should be noted that the described results for the ion-beam treatment of the diamond surface are not common. The high-fluence ion irradiation of most metals and semiconductors leads to a significant development of ordered (in the form of ripples) and stochastic reliefs (in the form of cones, pyramids, ridges, etc.). The ion irradiation of graphite-like carbons also leads to a significant development of the relief. In particular, the irradiation of highly oriented pyrographite, which is the closest in structure to a single crystal of graphite, leads to an extreme development of microrelief in the form of sharp ridges of micron size in a temperature range for the irradiated samples from room temperature to 400 ◦C [21]. Such a strong effect of the temperature of the irradiated diamond samples on the ion-induced relief was not observed. In particular, the ion-induced relief after irradiation with argon ions with an energy of 30 keV at temperatures of 230 and 400 ◦C is practically the same [22].

### *3.3. Raman Spectroscopy*

It is known that Raman spectroscopy (RS) is an effective method for studying carbon materials [23]. In RS spectra in the frequency range 1000–1700 cm<sup>−</sup>1, diamond gives a single narrow peak at 1332 cm−1, and graphite-like materials manifest themselves as characteristic D and G peaks, with frequencies for microcrystalline graphite of 1345 and 1580 cm−1, respectively. The Raman spectra of graphite-like materials can also contain peaks at the frequencies 1200, 1500 and 1620 cm−1. These peaks appear for disordered or nanocrystalline graphite-like materials and are associated with the disorder of the planar structure of crystallites, boundary scattering when crystallites are reduced to nanometer sizes, disorder of translational symmetry, ionic impurities in materials and formation of carbyne chain compounds.

Raman spectroscopy data obtained after the ion irradiation of polycrystalline diamond are shown in Figure 4. Ion-induced graphitization under irradiation with argon ions manifests itself in the RS spectra in the form of broadened D and G peaks. The diamond peak is also observed due to the optical transparency of a thin ~30 nm graphite-like layer. The intensity ratio *I*D/*I*<sup>G</sup> and the positions of the D and G peaks correspond to graphite with a high concentration of radiation damage [24].

**Figure 4.** Raman spectra for chemical vapor deposition (CVD) diamond before and after irradiation by 30 keV Ar<sup>+</sup> and C<sup>+</sup> ions. Spectrum for polycrystalline graphite MPG-8 was measured for comparison. The Gaussian analyses of the spectrum are shown by thin lines for diamond irradiated with Ar<sup>+</sup> ions.

The Raman spectrum after irradiation with carbon ions shows that synthesizing a diamond surface with a size of ~0.1 μm practically does not result in a difference from the Raman spectrum of the initial diamond. This indicates a good crystallinity of the synthesized diamond layer upon the implantation of carbon ions. Similar results were obtained for single crystal diamond [12].
